Radially expandable vascular stent

ABSTRACT

The invention relates to a radially expandable stent comprising a plurality of ring elements ( 2, 3, 27, 28 ) which are flexibly connected to each other by means of bending elements ( (18, 20, 21 ) and which define the inventive stent ( 1 ) which is provided with a proximal end, a distal end and a longitudinal axis. The ring elements ( 2, 3, 27, 28 ) are arranged next to each other in a perpendicular position with respect to the longitudinal axis of the stent ( 1 ) and are respectively connected to each other by means of flexible bending elements ( 18, 20, 21 ). On the proximal and distal end of the stent ( 1 ), the ring elements ( 27,28 ) respectively located on the edge thereof are joined to each other by a pair of dumbbell-shaped bending elements ( 18 ). Ring elements ( 2,3 ) located in the centre thereof are joined to each other and respectively connected to the ring elements ( 28 ) on the edge thereof by two s-shaped bending elements ( 20,21 ). At least the bending elements ( 2,3 ) in the centre are embodied in the form of a zig-zag.

[0001] The invention relates to a radially expandable vascular supportto be utilized to keep blood vessels or other paths of organs open inhuman or animal bodies. This grid-shaped vascular support is comprisedof several tubular elements with a mainly zigzag-shaped annularstructure of small width, the rings of which are linked bydumbbell-shaped or S-shaped bars.

[0002] Patent EP 335 341 B1 describes vascular supports that are formedof elongated pairs of members. These vascular supports are implanted,for example, in contracted or other body vessels to keep thempermanently open after a balloon dilatation. The vascular supports arethereby expanded in their diameter and contract in their lateral length.As a rule, this contraction is undesirable because it may cause a wrongpositioning of the vascular support. Known vascular supports adaptthemselves relatively poorly or not at all to bows or curves in thecourse of a vessel, thus calling for provision of additional bendingelements.

[0003] Known vascular supports exhibit rigid tubular segments, which arelinked to each other somewhat more resiliently through hinged connectingpieces. In these areas, however, hypertrophies of the vascular wall mayoccur due to the special stresses imposed on the wall on every movementof the vessel. Other known vascular supports exhibit a considerablecontraction, particularly if expanded in the range of their maximumdiameter.

[0004] Vascular supports with bow-shaped, equidirectional bars betweenzigzag-shaped annular elements, for example, are known from patent DE197 40 506 A1. But due to numerous bars between annular elements,vascular supports of that type are very rigid and inflexible, whichmight involve failures when implantation is attempted in case of acurved vessel course.

[0005] On account of the numerous bow-shaped bars, it might also happenthat side branches of the vascular system are unintentionally blocked,although they should remain open.

[0006] The equidirectional bow-shaped bars on the circumference alsobear the disadvantage that this vascular support, in case of a curvedcourse of the vessel, easily bends and partly or wholly blocks thevessel, which should be kept open by the vascular support.

[0007] Now, therefore, it is the task of the present invention to createa radially expandable vascular support which during its expansion issubjected to no or just a small contraction, and which bends less easilywhile being better suited to a curved vessel course, and which, at thesame time, exhibits adequate radial stability. Likewise, in its expandedstatus, the vascular support should exhibit sufficiently largecross-sections between the various bars to keep lateral branches of thevascular system open.

[0008] This task for said vascular support is solved in that thevascular support exhibits a plurality of annular elements flexiblyconnected to each other by means of bending elements, said annularelements defining a vascular support with a proximal and a distal endand a longitudinal axis, with said annular elements being arranged sideby side transversely to the longitudinal axis of the vascular supportand being linked to each other by bending elements, and wherein at leasttwo annular elements each standing at the margin are linked to eachother at the proximal and distal end of the vascular support by a pairof dumbbell bending elements, and wherein annular elements standing inthe center are linked among each other and with marginally-standingannular elements by two S-shaped bending elements each, with at leastthe centrally-standing annular elements having a zigzag shape.

[0009] Upon radial expansion of the vascular support, the bendingelements stretch along the longitudinal axis, in conformity with lateralcontraction of the zigzag-shaped annular elements, thus avoiding orreducing an overall contraction of the vascular support. According tothe present invention, the S-shaped bars at central annular elements arearranged in pairs each, thus providing for an especially highflexibility in the central area. The S-shaped supports are expedientlyarranged in pairs in such a manner that they face each other on thecircumference of the vascular support. The S-shaped bending elements maybe arranged equidirectional or oppositely directional; because of thehigher stability, preference is given to an equidirectional arrangement,but oppositely directional arrangements may also be provided for toincrease flexibility.

[0010] At the proximal and distal end of the vascular support being thesubject of this invention, there are two or more marginally standingannular elements each, which are linked among each other by a pair ofdumbbell bending elements. These marginally standing annular elementsare expediently shaped like a serpentine line, with two adjacentmarginally standing annular elements expediently pointing to each otherwith their bows. In the area of these bows pointing to each other, onoppositely facing sides of the circumference, there are straightconnecting bars of a somewhat dumbbell design. The serpentine-likedesign of the marginally standing annular elements in conjunction withthe straight connecting and/or bending elements gives greater rigidityto the vascular support in its marginal areas that is beneficial to thestability at the vascular wall and allows for a reliable anchoring.

[0011] In the sense of the present invention, the term “dumbbell shaped”designates those bending elements, which have the shape of an upright,lying or oblique S or that of a mirror-inverted S. The term“equidirectional” means that the S-shaped or other elements on thesurface of the vascular support are equally orientated in the planarrepresentation.

[0012] Expediently the zigzag-shaped annular elements are rounded-off attheir ends each to form bows. The width of the zigzag-shaped annularelements in the area of the bows may be greater than that in the area ofthe bars.

[0013] Furthermore, to increase stability in the various areas,particularly towards the lateral end of the vascular support, the widthof the bars and/or that of the zigzag-shaped annular elements may begreater than that in other areas, particularly in the central area. Onthe other hand, to increase the radial force in the central area of thevascular support, the width of bars and/or bows of the zigzag-shapedelements in the central area of the vascular support may be greater thanthat at its ends. The various types of design each depend on theintended purpose, course of the vessel, branches of the vessel, if any,and similar factors. In this way, it is feasible to achieve broadvariability with reference to adaptability and radial stability.

[0014] The vascular support which is expandable according to the presentinvention is expediently built-up in its central area in such a way thatthe zigzag-shaped annular elements are equidirectionally orientated withtheir bows, that means all bows point into the same direction at alllevels. The same is valid for the bows of adjacent serpentineline-shaped and zigzag-shaped annular elements, thus making it possibleto arrange the S-shaped bending elements diagonally staggered over thevascular support to create a spiral shape. Thereby, the vascular supporthas a preferred bending direction from annular element to annularelement.

[0015] The S-shaped bending elements used according to the presentinvention at the zigzag-shaped annular elements are mainly arranged invertical direction, that means they mainly run vertically to the bars ofthe zigzag-shaped annular elements. The vascular supports of thisconfiguration thereby attain utmost flexibility. To obtain additionalstability in longitudinal direction, however, it may make sense toorientate the S-shaped bending elements mainly in parallel to the barsand bows of the zigzag-shaped annular elements. Good compensation forcontraction in length is thus achieved on expanding the vascularsupport.

[0016] The bending elements between the various annular elementspreferably exhibit a somewhat smaller cross-section than the straightbar area of the zigzag-shaped annular elements, expediently by 10 to50%, and particularly by about 30%.

[0017] Furthermore, the zigzag-shaped annular elements may exhibitdifferent cross-sections at the edge and in the central range of thevascular support. To improve the supporting properties and radialstrength at the edge, the vascular support may exhibit a larger width ofthe bars at both ends. To improve the local supporting properties in thearea of the focal vessel narrowing and the radial strength, on the otherhand, the vascular support exhibits a larger width of the bar and/or alarger cross-section in the central area only. An electro-polishingprocess which removes less material, for example, may achieve the largercross-section in the central area.

[0018] The bending behaviour of the vascular support on crimping andexpansion may be further improved by a particular configuration of thebows of the zigzag-shaped annular elements, for example C-shaped, orhairpin-shaped, or bracket-shaped, particularly if the width of theC-shaped or bracket-shaped bow is smaller than that of the bar of thezigzag-shaped annular element.

[0019] Preferably usable as material for the vascular support are one ormore biocompatible materials of the group niobium, platinum, steel,titanium, a nickel-titanium alloy, platinum-iridium, or an alloy madefrom at least one of these metals like platinum-iridium with suitableweight percents. If the vascular support is to be self-expendable, anickel-titanium alloy (Nitinol) is preferably used which istemperature-optimized by thermal treatment.

[0020] To improve the growth into the vascular wall, the metal may becoated with a biocompatible material or with suitable medicaments toavoid hyper-proliferation of the vessel, or may produce radiation byradioactive decay after irradiation or input of a radioactive materialinto the body or coating.

[0021] Moreover, the vascular support may be comprised of resorbableplastic material, e.g. aliphatic polyesters like polydioxanon.

[0022] If the vascular support is to be used for a splinting ofaneurisms, it is preferably provided with a biocompatible fabric braidedor sewn onto it, made from polyurethane, silicone, Teflon or polyester,or a thin foil made from one of these materials is sewn, welded, shrunkor glued to it.

[0023] The tubular bodies made from metal or plastic material arepreferably formed from seamlessly drawn tubes in order to avoid stressand cracks, as would be the case in the vicinity of welding seams. Thestructures are preferably produced by laser beam cutting, water jetcutting, electro-erosion and electro-polishing.

[0024] Embodiments of the present invention are further explained in thefollowing by way of a drawing, where:

[0025]FIG. 1 shows a preferred embodiment with snake-shaped annularelements in the outer area linked by dumbbell shaped bars, andzigzag-shaped annular elements in the central area linked by moreflexible S-shaped bars.

[0026]FIG. 2 shows a variant of the embodiment of FIG. 1, and

[0027]FIG. 3 shows various shapes of bending elements.

[0028] Apart from serpentine lines, all of the vascular supports shownin these figures exhibit zigzag-shaped annular elements with S-shapedconnecting elements. For clarity's sake, these figures represent theunrolled grid structures of the tube-shaped vascular supports.

[0029]FIG. 1 shows a preferable embodiment of the invention with twosnake-shaped annular elements 27, 28 each in the outer area which arelinked by two dumbbell shaped bars 18 each, and zigzag-shaped annularelements 2, 3 in the central or middle area which are linked to eachother by two more flexible S-shaped bending elements 20. The S-shapedbars or bending elements 20 and the zigzag-shaped annular elements 2, 3each are arranged equidirectonally. Concerning the orientation of bows7, 8, the annular elements 2 and 28 also run equidirectionally, whilethe annular elements 27 and 28 run in opposite direction.

[0030] Thus achieved is a great flexibility in the central area 24. As apeculiarity of this picture, the arches 7 of the individual annularelements 2, 3 which are open to the right, are arranged on an equallevel. Upon expansion of this structure, the individual S-shaped bars 20which will then expand, together with individual straight bars 9 lyingthere between and belonging to the zigzag-shaped annular elements 2, 3form a revolving, stable double helix structure.

[0031]FIG. 2 shows a variant of the design of FIG. 1, in which theS-shaped bending elements 21 run equidirectionally with the bars 9 andbows 7 of the zigzag-shaped annular elements 2, 3, that means thegeneral orientation and the course of the annular elements 2, 3 in thebending elements 21 continues.

[0032]FIG. 3 shows different variants of bending elements 18, 21 and 22that may be used. The dumb-bell shaped bending elements 18 according to(a), (b) and (c) differ by their length between the bows 8 of theannular elements 27 and 28. FIG. 3 (d), (e), (f) and (g) show differentshapes of S-shaped bending elements 20 and 21. As a matter of fact,these shapes may also be of a mirrored configuration.

[0033] From the above description and representation of the examples ofembodiments presented it becomes evident that the present invention isnot confined to the combinations of features designated in the claims orthe description, but rather that within the framework of the invention,other combinations of the features specified may be conceivable.

1. A radially expandable vessel support having a multitude of annularelements (2,3,27,28) flexibly connected to each other, defining avascular support (1) with a proximal and a distal end and a longitudinalaxis, wherein said annular elements (2,3,27,28) are arranged side byside transversely to said longitudinal axis of the vascular support andconnected to each other by means of bending elements (18,20,21),characterized in that at least two marginally standing annular elements(27,28) each are linked among each other by a pair of dumbbell shapedbending elements (18) and that centrally standing annular elements (2,3)are linked among each other and to marginally standing annular elements(28) by two S-shaped bending elements (20,21) each, with at least thecentrally standing annular elements (2,3) being of a zigzag-shapedconfiguration.
 2. A radially expandable vascular support pursuant toclaim 1, characterized in that the relevant bending elements (18,20,21)between two annular elements (2,3,27,28) form a pair of bending elementslying opposite to each other on the circumference.
 3. A radiallyexpandable vascular support pursuant to one of the claims 1 or 2,characterized in that at the proximal and distal end of said vascularsupport (1) there are two marginally standing annular elements (27,28)having a serpentine line-shaped course and having the dumbbell-shapedbending elements (18) at bows (8) pointing to each other.
 4. A radiallyexpandable vascular support pursuant to one of the claims 1 to 3,characterized in that the width of the S-shaped bars (20,21) is by 10 to50%, preferably by about 30% smaller than the width of bars (9) of thezigzag-shaped annular elements (2,3).
 5. A radially expandable vascularsupport pursuant to one of the claims 1 to 4, characterized in that thezigzag-shaped annular elements (2,3) are rounded-off at their ends togive them the shape of a bow (7).
 6. A radially expandable vascularsupport pursuant to one of the claims 1 to 5, characterized in that thewidth of the zigzag-shaped annular elements (2,3) in the area of bows(7) is larger than that in the area of bars (9).
 7. A radiallyexpandable vascular support pursuant to one of the claims 1 to 6,characterized in that the width of bars (9) and/or bows (7) of thezigzag-shaped annular elements (2,3) at the lateral ends of the vascularsupport (1) is larger than that in the central area.
 8. A radiallyexpandable vascular support pursuant to one of the claims 1 to 6,characterized in that the width of bars (9) and/or bows (7) of thezigzag-shaped annular elements (2,3) in the central area of the vascularsupport (1) is larger than that at the ends.
 9. A radially expandablevascular support pursuant to one of the claims 1 to 8, characterized inthat the zigzag-shaped annular elements (2,3) with their bows (7) areequidirectionally orientated.
 10. A radially expandable vascular supportpursuant to one of the claims 1 to 9, characterized in that the S-shapedbending elements (20,21) are diagonally staggered over the vascularsupport (1) so as to create a spiral shape.
 11. A radially expandablevascular support pursuant to one of the claims 1 to 10, characterized inthat the S-shaped bending elements (20) between the zigzag-shapedannular elements (2,3) are mainly arranged in vertical direction.
 12. Aradially expandable vascular support pursuant to one of the claims 1 to10, characterized in that the S-shaped bending elements (21) between thezigzag-shaped annular elements (2,3) are mainly orientated in parallelto said bars (9) and bows (8) of the zigzag-shaped annular elements(2,3).
 13. A radially expandable vascular support pursuant to one of theclaims 1 to 12, characterized in that it is essentially made of steel,tantalum, titanium, niobium, platinum, or of an alloy consisting of atleast one of these metals and at least another one of these metals orother metals.
 14. A radially expandable vascular support pursuant toclaim 13, characterized in that it is made of a nickel-titanium alloywhich has been made self-expandable by way of thermal treatment.
 15. Aradially expandable vascular support pursuant to one of the claims 1 to12, characterized in that it is made of a resorbable material,preferably a plastic material.
 16. A radially expandable vascularsupport pursuant to one of the claims 1 to 15, characterized in that itis coated with a biocompatible material.
 17. A radially expandablevascular support pursuant to one of the claims 1 to 16, characterized inthat it is coated with suitable medicaments to avoid intimate hyperproliferation of the vascular wall.
 18. A radially expandable vascularsupport pursuant to claim 17, characterized in that the coating slowlyreleases the medicaments suitable to avoid intimate hyper proliferationof the vascular wall.
 19. A radially expandable vascular supportpursuant to one of the claims 1 to 16, characterized in that it iscoated with a radioactive material, which releases a radioactiveradiation to avoid or reduce hyper proliferation of the vascular wall.20. A radially expandable vascular support pursuant to one of the claims1 to 16, characterized in that it is provided with a biocompatiblefabric made of polyurethane, silicone, Teflon, or polyester, or with athin foil made of one of these materials.